1. Field of the Invention
This invention relates to plastic bags having releasable closures, and more particularly, to an improvement which makes the bags resistant to accidental opening of the closure.
2. Cross-Reference to Related Application
Application Ser. No. 433,614, filed Oct. 12, 1982 (now U.S. Pat. No. 4,419,159) "Manufacture of Plastic Bags With Interlocking Profile Extrusions", Herrington, filed concurrently herewith, discloses and claims the manufacturing process which can be used in the manufacture of the bag of this invention.
3. Description of the Prior Art
Various closure arrangements have been employed for closing plastic bags. U.S. Pat. No. Re. 28,969-Naito shows the Zip-loc storage bag in which a profile extrusion on one side of the bag mates with a profile extrusion on the other side of the bag to form an interlocking, reclosable, closure.
U.S. Pat. No. 4,212,337-Kamp shows another example of a closure for a plastic bag in which the closure is formed by extruded protrusions on opposing bag surfaces which interlock to form a releasable, reclosable, closure. This patent recognizes the problem of making a closure which is easily releasable when force is applied externally to the bag, but which resists opening when force is applied to the closure by the contents of the bag. The patent suggests a solution in which the closure has a "negative angle of engagement" inside of the container and a "positive angle of engagement" on the outside of the bag. The extrusion of profiles having different engagement angles is difficult, it being much easier to extrude symmetrical, uniform profiles. The closure of the Kamp patent is attached to the heat-sealable film in a separate step after the manufacture of the film. Heat is transferred through the film to produce melting at the interface of the film and the closure to attach the closure to the film. This type of attachment is a slow process which cannot practically be performed in-line with the extrusion and bagmaking.
It is an object of the present invention to provide a closure for a plastic bag which resists opening by the contents from inside the bag, but is easily opened by hand from the outside.
It is another object of the present invention to provide a plastic bag with extruded locking profiles which are heat sealed to the plastic film during an in-line bag manufacturing process.